Application of Atomic Layer Deposition on ZnO Nanorod Arrays
Date Issued
2010
Date
2010
Author(s)
Yeh, Yu-Cheng
Abstract
In this thesis, it can be divided into three different topics. The first topic is the influence of different shell layer on optical properties of ZnO nanorod arrays. The second topic is about magnesium doping to ZnO NRAs. The third topic is effect of heat treatment on ZnO NRAs based light-emitting-diodes.
In Chapter 2, we report that, after coated with Al2O3 shell, surface band bending of ZnO NRAs was lowered while causing strong wave function overlap around surface. In consequence, near-band-edge (NBE) emission was enhanced. On the other hand, visible luminescence band in photoluminescence (PL) spectra changed after coated with ZnO shell. The luminescence mechanism was investigated. The result indicated that green luminescence involved V_O^∙ centers trapping photo-generated holes then recombined with electrons from conduction band. And yellow luminescence was attributed to defect state in the “bulk” of ZnO core.
Chapter 3 describes a simple way to dope ZnO NRAs with magnesium. MgZnO nanorod arrays were successfully fabricated through annealing ZnO/MgO core-shell structure. Near-band-edge emission in PL spectra blushifted as annealing temperature increased. Carrier localization in the coaxial structure is reported. Due to difference in core/shell bandgap energy, carrier could be confined in the core of nanorod and non-radiative recombination caused by surface state effect would be suppressed. We verified carrier localization through examining thermal quenching.
In chapter 4, ZnO film/ZnO nanorod arrays/GaN layer heterojuction LEDs were fabricated and effect of heat treatment was investigated. Light emitting under reverse bias was observed and resulted from electron tunneling. Rapid-thermal-annealing (RTA) treatment “blur” ZnO/GaN interface and respond for formation of deep-level states at the interface. Visible luminescence in electroluminescence (EL) was observed with RTA treatment. Characteristics of type Ⅱ band alignment were shown when no heat treatment was conducted. I-V curve shows large tunneling current at small applied reverse bias. Tunneling of electrons from valence band of ZnO to conduction band of ZnO was proposed, and EL mechanisms were investigated in detail.
Subjects
ZnO
nanorod arrays
atomic layer deposition
light-emitting diode
Type
thesis
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